Is oil actually good for sea life?

Where oil seeps naturally from the seabed and bubbles up to the surface, phytoplankton thrive, according to new research. But this doesn't mean that oil, wherever it comes from, is always a biological boon.

Oil can be seen in the Gulf of Mexico, April 2010, more than 50 miles southeast of Venice on Louisiana's tip, as a large plume of smoke rises from fires on BP's Deepwater Horizon offshore oil rig.

Gerald Herbert/AP

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Naturally occurring oil vents in the sea floor, releasing hundreds of thousands of barrels of oil into the Gulf of Mexico each year, may actually benefit living organisms, states new research published Monday in Nature Geoscience.

As well as considering the impact of oil seepage itself, the researchers drew comparisons with the impact of oil released by the 2010 Deepwater Horizon spill.

With regard to Deepwater Horizon, the amount of oil pouring into the Gulf of Mexico totaled 4.3 million barrels, compared to an annual natural rate of 160,000 to 600,000 barrels.

"This information gives us context for the Deepwater Horizon spill," said co-author Ian MacDonald, an oceanographer and professor at Florida State University. "Although natural seeps are significant over time, the spill was vastly more concentrated in time and space, which is why its impact was so severe."

One of the first insights came as lead author Nigel D’Souza, then a postdoctoral researcher at Columbia University, was cruising over the Gulf of Mexico in a ship, observing chlorophyll fluorescence, a characteristic of certain phytoplankton.

In what he described as “a eureka moment,” he noticed how much more abundant the phytoplankton were when found above natural oil seeps.

In fact, they were almost twice as concentrated as phytoplankton found even a few kilometers away.

In seeking to explain this effect, the researchers say it is unlikely to be the direct impact of oil itself, says Andrew Juhl of Columbia University’s Lamont-Doherty Earth Observatory and coauthor of the study, in a telephone interview with The Christian Science Monitor.

“In general, oil seems to be uniformly negative for phytoplankton in terms of its direct effect.”

So why the explosion of life above the sea vents? The answer lies in a “peculiar interaction of different things,” says Dr. Juhl.

Deep water is heavily laden with nutrients, usually inaccessible to life-forms living near the surface. But as oil bubbles up from the seabed, it agitates these nutrients and carries them upwards.

It is, therefore, this nutritional boost that allows the phytoplankton to thrive.

So, does this mean that oil spills are a good thing, after all? Hardly, according to Juhl.

“If you had an anthropogenic oil spill from a tanker or pipeline, you wouldn’t have the positive effects of oil because it wouldn’t be carrying with it the nutrient-rich water,” says Juhl.

“Above a natural oil seep, you can see a sheen of oil on the water, you can even smell it on the surface, but it’s still a very small amount of oil in comparison to the kind of oil spills that make the news.”

What makes this research so interesting, then, is not any reversal on our understanding of how damaging oil spills can be. Instead, it marks the first time research has been able to draw conclusions between what happens at oil vents, deep down on the ocean floor, and the effects near the water’s surface, sometimes with a mile of water separating the two.